Allow contact data clean-up to be activated independently of auto-trash feature

Our current data retention policy feature allows conversations to be automatically hard-deleted after a period of time, and then associated contact data is cleaned up when all related conversation data has been deleted.

This improvement would allow the automatic hard-deletion and contact data cleanup to be activated independently of each other. This allows

• Conversation data to be automatically cleaned up, without also deleting contacts. This could be useful if a customer does not require full GDPR compliance but does not want to retain message content indefinitely

• Contact clean up can be used in conjunction with other workflows to delete old conversations. In particular, if a customer has a data retention policy feature in gmail or outlook, and a hard-deletion sync with Front.